The present invention concerns a method and apparatus for increasing nerve conduction velocity by the application of uniquely shaped electrical pulses to the nerve system of the human body in order to alleviate nerve disorders caused by disease, physical trauma or chemical trauma. The unique shape of the electrical pulses is derived from a Fourier analysis of nerve bio-potentials.
It has been well established that electric stimulation of nerves with low-level electrical pulses (Transcutaneous Electric Neural Stimulation--TENS) is of enormous value for the symptomatic relief of pain. TENS devices have been used primarily for temporary pain relief. Pain and sensory input signals are generated at specific sites in the body and transmitted to the brain through the propagation of ionic conduction in nerves. Pain is sensed in the brain as a result of the propagation of pain signals through the nerves to the brain. If a TENS device is placed between the location of pain and the brain and the electrical signal of the TENS is larger than the pain signal, the brain will sense primarily the TENS signal. This method of pain blocking has been somewhat successful because it decreases the use of drugs, however, the relief of pain for most cases is only temporary. When the TENS device is removed, the pain will reappear if the source of pain has not been changed, similar to the affect of a local anesthetic.
Looking further at the nerve cell, a small excess of negative ions called anions accumulates immediately inside the cell membrane along its inner surface, and an equal amount of positive ions called cations accumulates immediately outside the membrane. The resultant charge or force of these ions produces what is called the membrane potential between the inside and outside of the nerve cell. The membrane potential can change by either an active transport of ions through the membrane, thus creating an imbalance of negative and positive charges on the sides of the membrane or the diffusion of ions through the membrane as a result of ion concentration differences between the two sides of the membrane, which also creates an imbalance of charges. The process of active transport is the moving of ionic molecules against a concentration or pressure gradient. Diffusion is the continual movement of molecules among each other in liquids or gases resulting in a homogeneous distribution or mixing of molecules. Minute quantities of sodium and potassium ions can diffuse through the pores of the cell membrane. If such diffussion should take place over a long period of time, the concentrations of the two ions would eventually become equal inside and outside the cell. This is why the active transport mechanism of sodium(+) and potassium(-) ions, called the sodium-potassium pump is so important. There are several theories of the precise mechanism of this pump, however, for this discussion it suffices to say that the mechanism carrier has the capability of splitting ATP (adenosine triphosphate) molecules and utilizing the resulting energy to transport sodium ions against concentration gradients of 20 to 1 and potassium ions against concentration gradients of 30 to 1. Calcium ions normally decrease the permeability of the membrane to sodium. If sufficient calcium ions are not available, the permeability of the membrane to sodium becomes increased thus increasing the membrane excitability--sometimes so greatly that spontaneous impulses may result and cause neuro-muscular spasm and/or pain. The abrupt changes in membrane potential, which can last a few ten thousandths of a second to a few thousandths of a second, are known as the action potentials, which are the means by which informational signals are transported from one part of the nervous system to another. They can be evoked in a nerve by any mechanism that suddenly increases the permeability of the membrane to sodium ions. This can be caused by electrical stimulation, mechanical compression of the fiber, chemical substances applied to the membrane, or any other event that disturbs the normal resting state (resting potential) of the neural membrane.
The design of TENS devices has been based on the premise that a sufficient amount of charge per unit area must be displaced across the cell membrane in order to raise the transmembrane potential to its firing threshold. Therefore, devices were designed to stimulate nerve cells with single or multiple pulses or spikes of variable width and frequency. Their effectiveness for pain relief varies and is temporary at best; effectiveness is nonexistant for increasing nerve conduction velocity. Poor nerve conduction velocity can result in such manifestations as: sensory deficit, poor neuro-muscular coordination, pain, vasular disorders, etc.